In recent years, dementia has become a significant medical problem worldwide. Dementia is a disease associated with various symptoms mainly including learning and memory disorders and impaired judgment, in which the symptoms and progression thereof vary depending on the causative diseases thereof. In any case, they are common in that they markedly impair the quality of life of the patients. In consideration of the fact that dementia forces huge labor to the caregivers including patients' families, it is a very serious social problem. It is predicted that the dementia patients will further increase hereafter in Japan, since an increase in the population of elderly people due to prolongation of life span is related to an increase in the dementia patients. In addition, there are many people suffering from cognitive impairment due to aging, which is not classified as dementia.
Various compounds capable of improving dementia have been reported. 8-[2-(2-Pentyl-cyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA), which is a linoleic acid derivative, is a compound having a long-term enhancing action on synapse transmission efficiency, which can delay metabolism in the body and can maintain stable LTP (long-teLm potentiation)-like enhancement of synapse transmission (patent document 1). LTP is considered to be involved in the onset of, for example, various neurological and mental diseases such as Alzheimer's disease and the like, and therefore, a substance that induces LTP expression has a possibility of providing a therapeutic or prophylactic drug for these neurological and mental diseases including dementia.
On the other hand, phospholipid has also been reported to be effective for the improvement of cognitive function and for neurodegenerative diseases. For example, 1,2-dilinoleoyl-sn-glycero-3-phosphocholine and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine have been reported to improve spatial learning disorder and memory disorder induced by scopolamine, or mild cognitive impairment and dementia (non-patent documents 1, 2).
Also, phosphatidylethanolamine is a phospholipid, which is one of the main components of biological membrane, and is being marketed along with phosphatidylserine and the like as health foods. Of phosphatidylethanolamines, particularly, dilinoleoyl•phosphatidylethanolamine (containing two linoleic acids as fatty acids) has been reported to have cell death induction suppressive activity, particularly, endoplasmic reticulum stress suppressive activity and, due to such activity, dilinoleoyl•phosphatidylethanolamine can be used for pharmaceutical application, particularly for the prophylaxis and/or treatment of neurodegenerative disease (patent document 2).
However, it is not known that a compound wherein an unsaturated fatty acid derivative having a cyclopropane ring such as DCP-LA and the like and phospholipid are bonded is effective for the improvement of cognitive function, and there is no report on the pharmacological effect provided by such compound.